1. Field of the Invention
The invention relates to a vehicular air-conditioning system which produces a flow of supply air the temperature of which has been adjusted using coolant of an internal combustion engine, and a control method of that vehicular air-conditioning system.
2. Description of the Related Art
In an air-conditioning system (hereinafter simply referred to as “air-conditioner”) provided in a vehicle having an internal combustion engine (hereinafter simply referred to as “engine”) as a driving source for running, supply air is heated using engine coolant that is circulated between a heater core provided as a heat exchanger for heating, and the engine. This engine coolant is circulated between the engine, an engine radiator, and the heater core by a water pump which is driven by the driving force of the engine.
Vehicles in which engine stop control is performed, which stops the engine when a preset engine stop condition such as idling stop is satisfied in an attempt to conserve energy and reduce emissions (hereinafter this control will simply be referred to as “eco-run control”), use an electric pump which is driven by an electric motor to enable engine coolant to still be circulated even when the engine is stopped.
A hybrid vehicle that is provided with an electric motor as well as an engine as a driving source for running is one such vehicle in which eco-run control is performed. These hybrid vehicles aim to improve fuel efficiency and reduce emissions by stopping the engine not only when the vehicle is stopped but also while the vehicle is running.
However, even in a vehicle in which eco-run control is performed, when the temperatures of the engine and the engine coolant are low at engine startup, the engine is first warmed up to a temperature at which it is able to run efficiently.
With an air-conditioner, if the temperature of the engine coolant is low as is the case when the engine is warming up, for example, the desired heating ability is unable to be obtained. If the heating ability is insufficient, low temperature (i.e., cool) air is blown out which may by unpleasant for occupants. Also, if the vehicle cabin starts to be heated using engine coolant while the engine is warming up, the engine coolant may end up being cooled by the heater core, thus lengthening the time that it takes for the engine to warm up.
This resulted in a proposal for technology to promote engine warm-up by suppressing the circulation of coolant when warming up the internal combustion engine.
For example, technology described in Japanese Patent Application Publication No. 10-18845 (JP-A-10-18845) aims to shorten engine warm-up time and enable heating to start earlier by reducing the flowrate of coolant that is circulated in the coolant circuit when the coolant temperature is equal to or less than a predetermined temperature.
Also, technology described in Japanese Patent Application Publication No. 6-72132 (JP-A-6-72132) stops blowing air until the temperature of the engine coolant has reached a set temperature selected according to the outside air temperature to prevent cool air from being blown out.
Meanwhile, in a vehicle that is running, the volume of supply air that is blown into the vehicle cabin changes according to the pressure (i.e., ram pressure) against the front of the vehicle, which may be unpleasant for the occupants. This resulted in a proposal of technology to correct the target supply air temperature based on the running speed of the vehicle and the ratio of outside air being introduced, which is described in Japanese Utility Model Application Publication No. 1-107610 (JP-U-1-107610).
In order to conserve energy when eco-run control is performed, it is necessary to increase the period of time for which the engine is stopped (i.e., the engine stop time), and inhibit the engine from being repeatedly stopped and restarted frequently. Further, even more energy can be saved by reducing the amount the electric pump is driven which reduces power consumption.
However, when the engine has been stopped for an extended period of time such that the temperature of the engine coolant drops and the electric pump is stopped, the heating ability of the air-conditioner also diminishes. Therefore, Japanese Patent Application Publication No. 2005-163545 (JP-A-2005-163545) proposes technology to start the engine when the temperature of the engine coolant drops, and stop the engine and drive the electric pump when the temperature of the engine coolant rises above a predetermined temperature.
However, air may be end up being blown from an air outlet due to the ram pressure while the vehicle is moving, even if a blower fan of the air-conditioner is not being driven when the electric pump is stopped while the vehicle is running. Even if the target supply air temperature is adjusted according to the vehicle running speed to prevent this from happening, cool air may still end up being blown out if the temperature of the coolant is low and the heating ability is insufficient.